Coded track circuit apparatus



Y 1 50 R. M. GlLSON 2,515,868

CODED TRACK CIRCUIT APPARATUS Filed July 1, 1949 W n- X 5 27 5 2H71Z--% g ES 16 fig; 01 c I bl,

Potential 0 JNVEN TOR. R05 M 61155011 B Y HIS ATTORNEY Patented July 18, 1950 UNITED STATES PATENT OFFICE CODED TRACK CIRCUIT APPARATUS Robert M. Gilson, Swissvale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application July 1, 1949, Serial No. 102,514

8 Claims. 1

My invention relates to coded track circuit apparatus of the type employed in railway signaling systems, and particularly to an improved polar coded track circuit possessing sensitive shunting characteristics and retaining broken rail protection.

It has been found that the shunting sensitivity of a track circuit may be increased by employing a high inter-rail voltage which is capable of breaking down any high resistance film which may form on the rail. However, the increase in inter-rail voltage decreases the broken rail protection afforded by a low voltage track circuit, since the higher voltage applied to the track circuit may cause sufiioient current to flow through the ballast around a broken point in the rail to cause the track relay to be picked up.

Accordingly, it is an object of my invention to provide a polar coded track circuit in which both high and low voltage impulses are alternately and recurrently supplied to the rails of the track section, the high voltage energy providing sensitive shunting characteristics, and the low voltage energy providing broken rail protection.

Another object of my invention is to provide a polar coded track circuit of the type described, in which the high and low voltages are supplied from the usual low voltage track battery.

A. further object of my invention is to provide a polar coded track circuit of the type described which affords a high degree of protection against broken down insulated joints.

Yet another object of my invention is to provide a polar coded track circuit of the type described, having two code following track relays which are selectively responsive to the high and low voltage impulses, and requiring concurrent operation of both relays to provide a clear signal over the stretch including the track circuit.

Other objects of my invention and features of novelt thereof will be apparent from the folowing specification taken in connection with the accompanying drawings.

In practicing my invention, I provide means at one end of a track circuit for supplying recurrent pulses of energy of alternate polarity from a low voltage track battery to the section rails. The pulses of one polarity are supplied directly to the rails from the battery, and the pulses of the other polarity are supplied from the bateery through an impulse transformer, which causes the pulse of energy to be of shorter duration and relatively higher voltage than the impulse which is supplied directly from the battery. At the other end of the track circui I Cir provide a high voltage code-following track relay and a low voltage code-following track relay, that is, one of the relays is calibrated to operate only when energy of relatively high voltage is supplied thereto, and the other relay is calibrated to operate when energy of relatively low voltage is supplied thereto. The code-following track relays are alternately connected across the section rails by a polar stick repeater relay governed by the track relays, so that when each of the track relays picks up, it operates the repeater relay to disconnect that track relay from the section rails and to connect the other track relay across the rails. A conventional type of code detecting apparatus is governed by contacts of the repeater relay, and the code detecting apparatus governs a signal which controls the movement of trailic into the section including the track circuit.

I shall describe one form of a polar coded track circuit embodying my invention, and shall then point out the novel features thereof in claims.

The associated drawing is a diagrammatic view of a polar coded track circuit embodying a preferred form of my invention.

Referring to the drawing, there is shown a sec; tion of railway track 2T having track rails I and 2, over which traffic moves in the direction indicated by the arrow, that is, from left to right. The section 2T is defined by the usual insulated joints 3 located at the entrance end W and the exit end X of the section.

The movement of trafiic into the section 2T is governed by a wayside signal 2S, here shown as a conventional color light signal having a green lamp 2G and a red lamp 23. Section ET is provided with a polar coded track circuit embodying my invention, comprising means at the exit end X of the track circuit for supplying recurrent pulses of energy of alternate polarity to the rails of the section, and means at the entrance end W of the track circuit for selectively detecting these pulses and governing the signal 2S accordingly.

The apparatus at the exit end X comprises a coding device ZCT, having contacts 10 and I2 which are recurrently operated between a first and a second position, an auxiliary code transmitting relay ZCTP, which is governed by the coding device ZCT, a track battery 2TB, and an impulse transformer 2TT having a condenser CI associated therewith. At the entrance end of the section there are provided two polar biased code-following track relays ZHTR and 2LTR, a polar stick code-following repeater relay ZTPR, a

first slow release relay ZFSA and a second slow release relay ZBSA.

In addition, there is provided at each end of the section a source of direct current energy, not shown, whose positive and negative terminals are designated as B and C, respectively.

With the equipment in its normal condition as is shown in the drawing, the coding device 2CT is continuously connected to the terminals '5 and C of the source, and as a result its contacts ill and [2 are recurrently operated at a selected rate, for instance Isl! times per minute. When the contact iii of coding device 2CT moves to its closed or picked up position, an obvious circuit is established for supplying energy to the winding of the auxiliary code transmitting relay ZCTP,

' which is of the code-following type. As a result,

relay ZCTP picks up its contact is. After a short time interval, contact ill of the coding device ZCT opens, and energy is no longer supplied to the winding of relay ZCTP. The relay ZCTP does not release immediately, however, due to the resistance snub it connected across the coils of the relay. This resistance snub causes the relay ZCTP to be slightly slow in releasing its contact, so that its contact 54 releases after a predetermined time interval has elapsed from theopening of contact N of the coding device ZCT. It will be seen that contact M of relay 201? is recurrently operated, with a short time interval elapsingbetween the release of the contacts of coding device ZCT and relay ZCTP.

The circuits are shown on the drawings in the position which they assume when the contact of coding device 2CT and relay ZCTP are both released. At this time, energy is supplied from the track battery 2TB to the primary winding is of the impulse transformer ZTT by a circuit which may be traced from the positive terminal of battery 2TB, over backcontact M of relay ZCTP, through the primary winding ill of impulse transformer ZTT to the negative terminal of battery 2TB, The current whichflows through the primary winding it of transformer ZTT causes energy to be built up in the magnetic field of the impulse transformer, and the condenser CI is connected across the terminals of the primary winding to improve this operation. Accordingly, it will be seen at this time that energy is being stored in the magnetic field of the impulse transformer ZTT.

When the coding device 2 C T picks up, its contact l2 establishes a circuit for connecting the secondary winding of transformer ZTT across the rails of section 2T. This circuit may be traced from rail, I, through the secondary winding 21} of transformer ZTT, over front contact l2 of coding device ZCT, and to rail 2 of section 2T. Shortly thereafter, relay 2C TP picks up, as previously described, and its back contact M interrupts the supply of energy to the primary winding of the impulse transformer ZTT. When the flow of current through the primary winding 18 of transformer 2TT is interrupted, an impulse of relatively high voltage and short duration is generated in secondary winding 29 by the rapid decay of the magnetic field of the impulse transformer, and this impulse is supplied to the rails of section 2T by the circuit previously traced,

since front contact l2 of coding device ZCT is closed at this time. The apparatus may be proportioned and arranged so that the duration of this high voltage impulse is somewhat shorter than the time interval during which the front contact l2 ofcoding device 2CT is closed, so that when the front contact I2 of coding device ZCT opens, it will not be required to break any appreciable current flowing through the circuit.

When coding device ZCT releases, the contacts of relay ZCTP remain picked up for a short interval thereafter, as previously explained. At this time therefore, a circuit is established over front: contact It of relay ZC'IP and back contact 52 of coding device 2CT to supply energy directly from the track battery 2TB to the section rails. The circuit may be traced from the positive terminal of battery 2TB, over front contact it of relay ZCTP, over back contact i2 of coding device ZCT to section rail 2, and from section rail 5 to the negative terminal of the battery 2TB. The apparatus is connected and arranged so that the high voltage impulse supplied from the secondary winding 2!) of the impulse transformer ZTT is opposite in polarity with respect to the section rails to the impulse of low voltage energy supplied directly from the battery 2TB. 1

Referring to. Fig. 2, there is shown a diagram which illustrates the relative polarities, magni tude and time ofthe high and low voltage impulses. It will be observed that the high voltage impulses are of the opposite polarity from the low voltage impulses, and additionally are of substantially shorter duration.

As long as the section ET is unoccupied, the equipment continues. tofunction in this manner, recurrently supplying pulses of alternate polarity to the rails of section 2T, the impulses of one polarity being of relatively high voltage of the opposite polaritywith respect to the other impulses.

Referring again to Fig: 1, the apparatus at the entrance endof the section 2T is shown in the condition which it assumes following the supply of the low voltage impulse of energy thereto. 0n the supply of the high voltage impulse of energy, energy is supplied from rail 5 of section 2T over reverse polar contact 22 of the repeater relay ZTPR, and through the winding of the code-following track relay 2HTR from left to right and back to rail 2 of section ET. The code-following relay ZHTR is constructed and arranged so that its contacts will pick up only upon the supply of energy through its winding in the direction indicated by the arrow, that is, from left to right, and additionally, the relay is calibrated so that it will not pick up its contacts from the supply of energy of the value of the low voltage impulses, but will only operate when energy of the magnitude of the high voltage impulses is supplied to the relaywinding. It will be seen that the supply of the high voltage impulse is such that the rail l is positive with respect to rail 2, which causes the current to flow through. the winding of relay ZI-ITR from left to right, and is of sufficient magnitude to cause the contacts to be picked up. When contact 24 of relay QHTR picks up, a circuit is established for supplying energy to the upper winding of relay 2TPR, which circuit may be traced from terminal B, over back contact 26 ofrelay ZLTR, over front contact 24 of relay ZHTR, and through the upper winding 23 of relay ZTPR to terminal C. The supply of energy to the upper winding 28 of relay ZTPR from left to right causes the contacts 22 and 32 of relay ZTPR to be operated to their normal or lefthandpositions. When contact 22 of relay 2TPR moves to its normal position, it interrupts the circuit. for supplying energy to the winding of relay ZHTR and establishes a circuit for supplying energy to the winding of relay ZLTR. The

relay ZTPR is of the polar stick type, having *stay-Where-put contacts, so that when relay ZI-ITR releases at the termination of the high voltage impulse, or by the opening of its circuit by contact 22 of relay 2TPR, whichever occurs first, and its contact 24 interrupts the circuit for supplying energy to the upper coil 28 of relay 2'I'PR, contact 22 will remain in its normal position.

When a low voltage impulse is supplied from the exit end of section ET, the energy flows from rail 2, through the winding of relay ZLTR from left to right, over normal contact 22 of relay ZTPR to rail I. The fiow of energy is in the proper direction and of sufficient magnitude to cause contact 26 of relay ZLTR to pick up, and a circuit is established thereby for supplying energy to the lower winding 38 of relay ZTPR, which circuit may be traced from terminal B over back contact 24 of relay ZHTR, over front contact 25 of relay ZLTR, and through the lower winding of relay '2'IPR from right to left to terminal C. As a result, the contact 22 of relay ZTPR is operated to its right-hand or reverse position, thereby disconnecting the relay ZLTR from the section rails, and establishing the connection of relay EHTP. to the section rails for the following impulse.

It will be apparent that the recurrent supply of high and low voltage impulses of alternate polarity from the rails of section 2T causes the alternate pick up and release of relays ZHTR and ZLTR, which in turn control the polar stick repeating relay ZTPR- to its normal and reverse positions.

A contact 32 of relay ZTPR governs a conventional decoding circuit comprising a first slow release relay ZFSA which is supplied with energy over reverse contact 32 of relay ZTPR, and a second slow release relay ZBSA which is supplied with energy by a circuit including normal contact 32 of relay ZTPR and front contact 34 of relay ZFSA. The relays 2FSA and ZBSA are constructed and arranged to be sufficiently slow in releasing their contacts so that they remain picked up during the intervals between the supply of energy to their windings. A contact 36 of relay ZBSA governs the supply of energy to the green lamp 2G of signal 2S when contact 36 is picked up, and when contact 38 of relay ZBSA is released, energy is supplied to the red lamp 2B of signal 28 and the supply of energy to the green lamp 2G- is cut oil.

' In its normal condition as shown on the drawings, with no train occupying section ET, the high and low voltage impulses recurrently supplied from the exit end of section 2T cause the apparatus at the entrance end of section 2T to operate in the manner described, so that the slow release relays 'ZFSA and are picked up, and energy is supplied to the green lamp 26 of signal 25, so that the signal indicates proceed.

When a train moving from left to right passes the signal is and enters section ET, the high voltage impulses will cause any rail film which may exist to be broken down, so that the wheels and axles of the train establish a shunt suificiently low in resistance to deprive the relay ZHTR of sufiicient energy to pick up and operate relay ZTPR to its normal position. The succeeding low voltage impulse even though it may not break through the rail film and be shunted by the wheels and axles of the train will not be applied to relay ZLTR. due to 2TPR not having been operated to its normal position by the preceding high voltage impulse. Neither will this low voltage impulse pick up relay EI-ITR as it is both of insufiicient magnitude and in the wrong direction.

As a result no energy is applied to the windings 28 and 30 of relay 2TPR after its first operation to its reverse position. The supply of energy to relay ZBSA is interrupted and it releases after a short time interval. In turn its contact 36 interrupts the supply of energy to the green lamp 2G of signal 26 and establishes a supply of energy to the red lamp 2R of signal 28, thereby causing the signal to indicate stop.

When the train moves out of section 2T, the supply of energy from the apparatus at the exit end over the rails l and 2 of section 2T to the apparatus at the entrance end is re-established. As previously described, the alternate supply of the high and low voltage impulses causes the recurrent and alternate operation of relays ZHTR and ZLTR, which in turn causes the repeater relay ZTPR to operate its contacts between a normal and reverse position. Energy is again supplied to the slow release relays 2FSA and ZBSA, and when contact SE of relay ZBSA picks up, it interrupts the supply or energy to the red lamp of signal 28 and establishes a supply of energy to the green lamp so that the signal again indicates proceed, and the equipment is thus restored to its normal condition.

As previousl pointed out, the code-following track relays 2HTR and ZLTR- are calibrated to respond to the high and low voltage impulses, respectively. Accordingly, should the rail I or 2 break at any point in the section 2T, the low voltage impulses will no longer be supplied to the winding of relay RLTR, or if supplied will not be of suflicient magnitude to cause the relay to pick up its contacts. As a result, only relay ZH'IR responds to the high voltage impulses, which causes the repeater relay ZTPR to be energized by current supplied through the upper winding 28 alone, resulting in contacts of relay QTPR moving to and remaining in their normal position. If contact 32 of relay ZTPR remains in its normal or left-hand position for longer than the normal interval between impulses, the relay EFSA will release and its contact 3 will interrupt the supply of' energy to relay 'ZBSA, which releases to cause the signal to display a stop aspect. Accordingly, it will be seen that the arrangement embodying my invention provides for broken rail protection, and additionally provides the high voltage impulses for securing sensitive shunting characteristics by causing the break-down of any high resistance film which may exist on the rail.

Moreover, the arrangement embodying my invention as shown in Fig. 1 is advantageous in that the relative polarities of adjacent track circuits may be staggered, so that a break-down of an insulated joint between the two adjacent sections will not cause improper operation of the code-following track relays associated with the one section by energy supplied through the broken-down joint from the apparatus at the exit end of the next section.

With broken down insulated joints and staggered relative polarities, energy from the track section to the left applied to section 2T would be positive on rail 2 for the high voltage impulses and positive on rail l for the low voltage impulses. With repeater relay ZTPR in its reverse position as shown in Fig. 1, the high voltage impulses from the adjacent section would be in the incorrect direction and the low voltage impulses would be of insufficient magnitude to pick up 7 relay Z-HTR. Relay ZTPR will, therefore, remain continuously in its reverse position removing energy from relay ZBSA and causing signal 28 to indicate stop. It is thus seen that broken-down (or defective) insulated joint protection is provided.

Although I have herein shown and described only one form of polar coded track circuit embodying my invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

j Having thus described my invention, what I claim, is:

1. In a coded track circuit railway signaling system, in combination, a section of railway track, means at one end of said section for recurrently supplying impulses of energy of alternate polarity to the rails of said section, the impulses of one polaritybeing of relatively higher voltage than the impulses of the opposite polarity, first code responsive means connected across the rails at the other end of said section and selectively responsive to the high voltage impulses of said one polarity, second code responsive means connected across the rails at the other end of said section and selectively responsive to the impulses of said other polarity, and code detecting means governed by the alternate and recurrent operation of said first and said second code responsive means.

2. In a coded track circuit railway signaling system, in combination, a section of railway track, energy supply means located at one end of said section for recurrently supplying to the rails of said section impulses of energy of alternate polarity, the impulses of one polarity being of substantially shorter duration and higher voltage than the impulses of the opposite polarity, said energy supply means comprising a coding device having contacts recurrently operated between a first and a second position, an auxiliary code transmitting relay having contacts operated between a first and a second position, said auxiliary relay being governed by said coding device so that the contacts of said auxiliary relay are operated to their first position when the contacts of. said coding device operate to their first posi tion and the contacts of said auxiliary relay are operated to their second position when the contacts of said coding device operate to their second position, an impulse transformer having a first and a second winding, a track battery, a first circuit for supplying energy from said battery to the first winding of said transformer including a first position contact of said auxiliary relay, a second circuit for supplying energy from said second winding of the transformer. to the section rails including a second position contact of said coding device, and a third circuit for supplying energy directly to the rails of said section from said battery including a first position contact of said coding device and a second position contact of said auxiliary relay, said impulse transformer being constructed and arranged so that the energy supplied therefrom to the section rails comprises a short impulse of high voltage opposite in polarity to the impulse supplied from said battery to the section rails, code responsive means located at the other end of said section for selectively responding to said impulses comprising, a first code following track relay calibrated to respond to said high voltage impulses but not to said low voltage impulses,

8'. l a second code following track relay calibratedto respond to said low voltage impulses, each of said code following track relays having a con-- tact which is operable between a first and a second position in response to the correct energization of the relay winding, a code following repeater relay governed by said code following trackv relays and having contacts which are operated to a first position when the contacts of said first. code following track relay are operated to their second position and which are operated to a second position when the contacts of said second code following track relay are operated to their second position, a fourth circuit for connecting said first code following track relay across, the section. rails including. a second position contact of saidrepeater relay, and a fifth circuit for connecting said second code following track relay across the section rails including a first position. contact of said repeater relay; and code detecting means for detecting the recurrent operation of voltage than the operated between a first and a second position,

said auxiliary relay being governed by said coding device so that the contact of said auxiliary relay are. operated to their first position when the contacts of said coding device operate to their first position and the contacts of said auxiliary relay are operated to their second position when the contacts of said coding device operate to their second position, an impulse transformer having a first and a second winding, a track battery, first circuit for supplying energy from said battery to the first winding of said transformer including a first position contact of said auxiliary relay, a second circuit for supplying energy from said second winding of the transformer to the sectionrails including a second position contact of said coding device, and a third circuit for supplying energy directly to the rails of said section from said battery including a first position contact of said coding device and a second position contact of said auxiliary relay, said impulse transformer being constructed and arranged so that the energy supplied therefrom to the section rails comprises a short impulse of high voltage opposite in polarity to the impulse supplied from said battery to the section rails; code responsive means located at the other end of said section for selectively responding to said impulses comprising, a first code following track relay of the polar biased type calibrated to respond to said high voltage impulses but not to said low voltage impulses, a second code following track relay of the polar biased type calibrated to respond to said low voltage impulses, each of said code following track relays having contact which is operable between a first and a second position in response to the supply of energy of proper magnitude and polarity to the relay winding, a code following repeater relay governed by said code following track relays and having contacts which are operated to a firstvoltage impulses will pass through the winding of the first code following track relay with the polarity required to operate the contact of said first code following track relay to its second position, and a fifth circuit for connecting said second code following track relay across the section rails including a first position contact of said repeater relay and arranged so that said low voltage impulses will pass through the wind-- ing of the second code following track relay with the polarity required to operate the contact of said second code following track relay to its second position; and code detecting means for detecting the recurrent operation of said re peater relay.

4. In a coded track circuit railway signaling system, in combination, a section f railw'aly track, energy supply means located at one end of said section for recurrently supplying to the rails of said section impulses of energy of alternate polarity, the impulses of one polarity being of substantially shorter duration and higher voltage than the impulses of the opposite polarity; said energy supply means comprising a coding device having contacts recurrently operated between a first and a second position, an auxiliary code transmitting relay having contacts operated between a first and a second position, said auxiliary relay being governed by said coding device so that the contacts of said auxiliary relay are operated to their first position when the contacts of said coding device operate to their first position and the contacts of said auxiliary relay are operated to their second position when the contacts of said coding device operates to their second position, an impulse transformer having a first and a second winding, a track battery, a first circuit for supplying energy from said battery to the first winding of said transformer including a first position contact of said auxiliary relay, a second circuit for supplying energy from said second winding of the transformer to the section rails including a second position contact of said coding device, and a third circuit for supplying energy directly to the rails of said section from said battery including a first position contact of said coding device and a second position contact of said auxiliary relay, said impulse transformer being constructed and arranged 50 that the energy supplied therefrom to the section rails comprises a short impulse of high voltage opposite in polarity to the impulse supplied from said battery to the section rails; code responsive means located at the other end of said section for selectively responding to said impulses comprising, a first code following track relay calibrated to respond to said high voltage impulses but not to said low voltage impulses, a second code following track relay calibrated to respond to said low voltage impulses, each of said code following track relays having a contact which is operable between a first and a second position in response to the correct energization of the relay winding, a code following repeater relay governed by said code following track relays and having contacts which are operated to a first position when the contacts of said first code following relay are operated to their second position and which are operated to a second position when the contacts of said second code following relay are operated to their second position, a fourth circuit for connecting said first code following track relay across the section rails including a second position contact of said repeater relay, and a fifth circuit for connecting said second code following track relay across the section rails including a first position contact of said repeater relay; code detecting means for detecting the recurrent operation of said repeater relay comprising a first and a second slow release relay, a sixth circuit for supplying energy to said first slow release relay when the contact of said repeater relay is in its second position, a seventh circuit for supplying energy to the winding of said second slow release relay when the contact of said repeater relay is in its first position and including a front contact of said first slow release relay, and traffic governing means con trolled by a contact of said second slow release relay.

5. In a coded track circuit railway signaling system, in combination, a section of railway track, energy suppl means located at one end of said section for recurrently supplying to the rails of said section impulses of energy of alternate polarity, the impulses of one polarity being of substantially shorter duration and higher voltage than the impulses of the opposite polarity; said energy supply means comprising a coding device having contacts recurrently operated between a first and a second position, an auxiliary code transmitting relay having contacts operated between a first and a second position, said auxiliary relay being governed by said coding device so that the contacts of said auxiliary relay are operated to their first position when the contacts of said coding device operate to their first position and the contacts of said auxiliary relay are operated to their second position when the contacts of said coding device operate to their second position, an impulse transformer having a first and a second winding, a track-battery, a first circuit for supplying energy from said battery to the first winding of said transformer including a first position contact of said auxiliary relay, a second circuit for supplying energy from said second winding of the transformer to the section rails including a second position contact of said coding device, and a third circuit for supplying energy directly to the rails of said section from said battery including a first position contact of said coding device and a second position contact of said auxiliary relay, said impulse transformer being constructed and arranged so that the energ supplied therefrom to the section rails comprises a short impulse of high voltage opposite in polarity to the impulse supplied from said battery to the section rails; code responsive means located at the other end of said section for selectively responding to said impulses comprising, a first code following track relay of the polar biased type calibrated to respond to said high voltage impulses but not to said low voltage impulses, a second code following track relay of the polar biased type calibrated to respond to said low voltage impulses, each of said code following track relays having a contact which is operable between a first and a second position in response to the supply of energy of proper magnitude and polarity to the relay winding, a

' and arranged so that said high voltage impulses will pass through the winding of the first code following track relay with the polarity required to operate the contact of said first code following track relay to its second position, a fifth circuit for connecting said second code following track relay across the section rails including a first position contact of said repeater relay and arranged so that said low voltage impulses will pass through the winding of the second code following track relay with the polarity required to operate the contact of said second code following track relay to its second position; code detecting means for detecting the recurrent operation of said repeater relay comprising a first and a second slow release relay, a sixth circuit for supplying energy to said first slow release relay when the contact of said repeater relay is in its second position, a seventh circuit for supplying energy to the winding of said second slow release relay when the contact of said repeater relay is in its first position and including a front contact of said first slow release relay; and traffic governing means controlled by a contact of said second slow release relay. I

6. In a coded track circuit railway signaling system, in combination, a section of railway track, energy supply means located at one end of said section for recurrently supplying to the rails of said section impulses of energy of alternate polarity, the impulses of one polarity being of substantially shorter duration and higher voltage than the impulses of the opposite polarity; said energy supply means comprising a coding device having contacts recurrently operated between a first and a second position, an auxiliary code transmitting relay having contacts operated between a first and a second position, said auxiliary relay being governed by said coding device so that the contacts of said auxiliary relay are operated to their first position when the contacts of said coding device operate to their first position and the contacts of said auxiliary relay are operated to their second position when the contacts of said coding device operate to their second position, an impulse transformer having a first and a second winding, a track battery, a first circuit for supplying energy from said battery to the first winding of said transformer including a first position contact of said auxiliary relay, a second circuit for supplying energy from said second winding of the transformer to the section rails including a second position contact of said coding device, and a third circuit for supplying energy directly to the rails of said section from said battery including a first position contact of said coding device and a second position contact of said auxiliary relay, said impulse transformer being constructed and arranged so that the energy supplied therefrom to the section rails comprises a short impulse of high voltage opposite in polarity to the impulse supplied from said battery to the section rails; code responsive means located at the other end of said section for 12 selectively responding to said impulses, and code detecting means for detecting the recurrent response of said code responsive means.

7. In a *coded track circuit railway signaling system, in combination, asection-of railway track, means at one end of said section for recurrently supplying impulses of energy of alternate polarity to the rails of said section, the impulses of one polarity being of relatively higher voltage, and

shorter duration than the impulses of the =oppo-' site polarity; code responsive means located at the other end of said section for selectively responding to said impulses comprising, a first code following track relay calibrated to respond to said high voltage impulses but not to said low voltage impulses, a second code following track relay calibrated to respond to said low voltage impulses, each of said code following track relays having a contact which is operable between a first and a second position "in response to the correct energization of the relay winding, a code following repeater relay governed by said code following track relays and having contacts which are operated to a first position when the contacts of said first code following relay are operated to their second position and which are operated to a second position when the contacts :of said secend code following relay are operated to their second position, a first circuit for connecting said first code following track relay across the section rails including a second position contact of said repeater relay, a second circuit for connecting said second code following track relay across the section rails including a first position contact of said repeater relay; and code detecting means for detecting the recurrent operation of said repeater relay.

8. In a coded track circuit railway signaling system, in combination, a section of railway track, means at one end of said section for recurrently supplying impulses of energy of alternate polarity to the rails of said section, the impulses of one polarity being of relatively higher voltage and shorter duration than the impulses of the opposite polarity; code responsive means located at the other end of said section for selectively responding to said impulses comprising, a first code following track relayof the polar biased type calibrated to respond to said high voltage impulses but not to said low voltage impulses, a second code following track relay of the polar biased type calibrated to respond to said low voltage impulses, each of said code following track relays having a contact which is operable between a first and a second position in response to the supply of energy of proper magnitude and polarity to the relay winding, a code following repeater relay governed by said code following track relays and having contacts which are operated to a first position when the contacts of said first code following track relay are operated to their second position and which are operated to a second position when the contacts of said second code following track relay are operated to their second position, a first circuit for connecting said first code following track relay across the section rails including a second position contact of said repeater relay and-arranged so that said high voltage impulses will pass through the winding of the first code following track relay with the polarity required to operate the contact of said first code following track relay to its second position, a second circuit for connecting said second code following track relay across the section rails including a first position contact of said 13 repeater relay and arranged so that said 10w volt- REFERENCES CITED age impulses will pass through the Winding of The following references are of record in the the second code following track relay with the file of this patent: polarity required to operate the contact of said second code following track relay to its second 5 UNITED STATES PATENTS position; and code detecting means for detect- Number Name Date ing the recurrent operation of said repeater 2,178,806 Place et a1 Nov. 7, 1939 relay. 2,362,678 Thompson Nov. 14, 1944 ROBERT M. GILSON. 

